Application of Sum-Frequency Generation Spectroscopy for the Structural Studies of Polyaniline

Abstract

Infrared-visible sum-frequency generation (SFG) vibrational spectra were obtained from the conducting form of polyaniline (PANI), emeraldine salt (ES). Observation of the SFG signal indicated the presence of oriented non-planar structures in ES. It was suggested that the additional resonant enhancement due to the absorption of the visible beam by the polymer film operated in the investigated system. Resonances characteristic to different structural units, benzenoid rings and polarons, were detected in the SFG spectra. The C-C stretching and C-H deformation vibrations of benzenoid rings were detected at 1623 and 1192 cm–1, while the polaronic ν(C~N+) vibrational mode was observed at 1336 cm–1. The stretching vibration of N-H bond was detected at 3273 cm–1 in the ssp-polarized SFG spectrum, indicating that the neighboring polymer chains in ES are connected by the N-H•••N interchain bridges.